1. Field of the Invention
The present invention relates to a caulking gun comprising a packing holder which has a longitudinal axis and is configured to accommodate a substantially cylindrical packing, said packing including an axially displaceable packing bottom, and said caulking gun further comprising a pressure disk.
2. Description of the Prior Art
Plastic substances, such as e.g. sealing compositions or adhesives, are made available for marketing by filling them into cartridges having an elongated cylindrical cartridge body. The cartridge body has a closed front end and an open rear end. Arranged at the front end is an end wall provided with a tubular projection or nozzle extending therefrom for pressing out the composition therethrough. The process of pressing out the substance from the cartridge is normally performed with the aid of a caulking gun. This tool includes a cartridge holder and an advancement mechanism for propelling an advancement rod carrying a pressure disk. The pressure disk will be inserted into the piston arranged in the cartridge. By actuating the caulking gun, the pressure disk will be intermittently or continuously advanced, thus extruding a quantity of substance from the cartridge via said tubular projection.
When substance is to be extruded out from a cartridge by advancement of a piston, it is important that the piston is sealed with the cylindrical cartridge wall. If the sealing function of the piston should be imperfect, a part of the substance may under the effect of the extrusion pressure be caused to flow past the piston and reach the pressure disk behind the piston. The substance leaking out in this manner will contaminate the caulking gun. Since the substance will harden or have an adhesive effect, it may even render the caulking gun unfit for use. At any rate, said leakage of substance often makes it necessary to perform an extensive cleaning process.
It is known that a piston arranged to be moved within a cartridge and made of semi-rigid plastic can be provided, in its interior, with an annular support lip engaging the transition region between the piston front face and the surrounding wall and having a shape tapering frustoconically towards the interior of the piston. When a press-on plate presses against the support lip, the piston is caused to be widened towards the outside in the edge region of the piston front face; thus, the piston will at least on its front piston shoulder be tightly pressed against a side wall of the cartridge. However, the side wall of the piston does not participate in said widening movement along its full length. If a quantity of the substance should happen to pass the piston shoulder, this quantity cannot be prevented anymore to pass also the complete piston and to get into contact with the caulking gun. Further, this arrangement will not allow the piston diameter to be widened by more than just a few tenths of a millimeter.
It is an object of the invention to provide an improved caulking gun wherein a rearward leakage of substance past the bottom of the packing and respectively past the piston is prevented.